1. Field of the Invention
The invention relates to computer cases and computers and more specifically, the invention relates to a low profile computer case and computer.
2. Description of the Related Art
As computers become more ubiquitous in society, it becomes more desirable to reduce the size of computer systems. Currently, there is a clear trend toward more powerful and more compact computer systems. Accordingly, the consumed power per unit density, i.e. the power density, of the average computer has increased tremendously over the past several years. However, such an increase in power density runs into a limitation of heat dissipation. More specifically, the higher the power density, the more heat generated and the more difficult it is to dissipate the heat. Of course, heat adversely affects the operation of most microprocessor based components and other computer components. Accordingly, the desire to reduce the size and increase the power of computers is at odds with the need to maintain components at temperatures within desired operating ranges.
Essentially, there are two processes by which heat in a computer case is dissipated. The first process is "air exchange cooling" which consists of replacing heated air in the case with cooler air, e.g. ambient air. The second process is "forced cooling" in which air is moved across the surface of a specific component to raise the convective heat transfer coefficient for the surface of the component thereby cooling the component faster than if the component was in static air. Most computer cases incorporate both heat dissipation processes to some degree. Both processes require the movement of air.
It is well known to use fans to move air through computer cases to cool various components therein. Conventionally, such fans are placed in a front panel or a back panel of the computer case. However, the desire to reduce the size of computers requires that front and back panel space be utilized efficiently for accessible components such as communication ports and power connections on the back panel, and removable media and fixed media drives on the front panel. Accordingly, the use of a fan in the front or back panel wastes precious panel space. Fans have been placed in side panels to avoid this problem. However, popular rack mount systems, such as systems complying with Engineering Industries Association Standard 310-C (EIA-310-C), require that the computer case be mountable in a rack having sides that closely oppose side panels of the computer case. Accordingly, side panels of the racks may interfere with operation of fans mounted in side panels of computer cases and thus the practice of mounting fans in side panels of computer cases has limited application. Further, it is often desirable to mount sliding rails on the computer case to permit it to be slid out of the rack for maintenance and the like. Such rails interfere with fans mounted in side panels. The use of shelves to avoid the need for rails restricts vertical room.
It is also known to provide one or more fans in an interior of a computer case. U.S. Pat. No. 5,793,610 is exemplary of references disclosing such an arrangement. U.S. Pat. No. 5,793,610 discloses a computer case having a support member in an interior of the case. Plural cooling fans are mounted in the support member. If one of the fans fails, air tends to re-circulate back through the opening in which the failed fan is mounted and thus a complex louver arrangement is provided.
U.S. Pat. No. 5,168,424 discloses a data storage unit having a housing and internal plate 105. Two open loop dc centrifugal fans are mounted in plate 105 to draw air from an area housing memory devices to an area housing a power supply. U.S. Pat. No. 5,168,424 uses dual entry open loop centrifugal fans to adjust for a variable impedance to air flow caused by varying numbers of memory devices on the upstream side of the fans. The downstream side of the fans contains only a power supply over which air flows to vents in a front panel and thus does not present significant impedance to the system. The intake ports of the fans are positioned opposite data storage devices. The use of two centrifugal fans having intake ports opposite devices requires a large amount of space in the chassis and thus the arrangement disclosed in U.S. Pat. No. 5,168,424 is not suitable for a low profile computer chassis which includes a motherboard and other components that require additional space in the chassis.
EIA-310-C, the disclosure of which is incorporated herein by reference, specifies three different rack sizes and the sizes and tolerances of cases that can be disposed in the racks in an attempt to insure that computers and components from various venders will fit in the same racks. There are three standard panel widths, i.e. rack sizes, 19", 24", and 30", with 19" being the most common. The vertical or height dimension of the racks is divided into a plurality of individual units known as a "U". In particular, one U equals 44.45 mm+0.4 mm. The horizontal or width dimension of a case for a 19" rack is 482.6 mm+0.4 mm. Many computer servers or the like are housed in a 6U case, i.e. a case that fits in the width dimension of the 19" rack noted above and is 265.9 mm high (44.45 mm.times.6=266.7 mm-0.8 mm tolerance to permit sliding the case into and out of the rack as prescribed by EIA-310-C).
In accordance with the recent trend in miniaturization, servers have been reduced to 2U cases, i.e. cases 88.1 mm in height. However, conventional 2U servers have at most four media drives in the front panel because of the need for fans and to allow for adequate air flow for forced cooling. While components, such as media drives have gotten smaller, at any given time they are designed to fit into standard form factors, such as "half height" drives (approximately 15/8" in height) and "low profile" drives (approximately 1" in height). Accordingly, case size and cooling considerations have limited the number of components, such as various media drives, that can be housed in a 2U case. Accordingly, the functionality and flexibility of conventional computers and computer components in 2U cases is limited.
It is important to utilize the limited width of EIA-320-C to its fullest extent also. Accordingly, conventional cases made to fit into standard EIA-310-C racks have side walls with a lip that extends across the top of the case to a small degree to allow a top panel to be screwed onto the lip from the top of the case thereby maximizing the width of the case. As noted above, many cases designed for rack mounting have slide out rails, i.e. drawer slides with rollers, that permit the case to be easily slid out of the rack and maintained in position for repair, maintenance and troubleshooting. The case including the slide out rails must fit within the standard rack width. Therefore, the use of rails, further limits the effective width of a case. Finally, an increased number of components results in an increased number of communication and power cables. If the cables are too bulky and not managed properly, they further restrict air flow and thus cooling. Cabling is one more consideration that puts increased component density at odds with cooling requirements.